Reversible color-changing sanitizer-indicating nonwoven wipe

ABSTRACT

A nonwoven wipe having a reversible sanitizer indicator for multiple uses and recharges is provided. The nonwoven wipe includes a cloth-like nonwoven fabric coated with a reversible color-changing ink formulation. During use, the nonwoven wipe is impregnated with a quaternary ammonium compound-based sanitizer. When the level of free quaternary ammonium compound falls below a threshold level, the color-changing ink formulation changes from a first color to a second color, indicating the need to recharge the wipe. When the nonwoven wipe is recharged with sanitizer solution, the color-changing ink formulation changes back to the first color.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/702,138, filed 8 Feb. 2010, which claims the benefit of U.S.Provisional Application No. 61/211,505 filed on 31 Mar. 2009. Theseapplications are herein incorporated by reference in their entirety andmade a part hereof.

FIELD OF THE INVENTION

The present invention is directed to a nonwoven wipe whose color changesfrom a first color to a second color when the concentration of sanitizerfalls below a threshold level, and changes from the second color back tothe first color when the concentration of sanitizer is again raisedabove the threshold level, for repeated cycles of use.

BACKGROUND OF THE INVENTION

Fabric wipes having color indicators are disclosed in U.S. Pat. No.4,311,479, issued to Fenn et al., and in U.S. Pat. No. 4,678,704, issuedto Fellows. Fenn et al. discloses a cloth impregnated with anantimicrobial composition that is activated upon contact with a liquidsuch as water, and is ionically bonded to the cloth. Small portions ofthe impregnated cloth are dyed with an indicator dye which bondspreferentially to the antimicrobial composition so that when theantimicrobial composition is exhausted, the dye will disappear from thecloth.

Fellows discloses an impregnated fabric material having an activecationic impregnant bonded to its fabric substrate. An anionic indicatordye in combination with a further cationic component is also bonded tothe substrate. The dye bonds to the further cationic component morereadily than to the substrate and the further cationic componentcompetes with the impregnant for bonding to the dye. In the case of awiping cloth, when the dye has been removed to indicate exhaustion ofthe active component, enough active component remains on the cloth toprovide a safety margin.

While these and similar prior art fabrics had color indicators toindicate the dissipation of impregnant, the indicators only worked once,and only changed color once. If the fabric was then recharged withimpregnant, such as by dipping it into a bucket, the original colorwould not return and the indicator function would not return. There is aneed or desire for fabrics impregnated with cleansing solutions,disinfectants and the like which can be recharged multiple times formultiple uses, and which indicate each time when the level of cleansingsolution or disinfectant becomes low.

SUMMARY OF THE INVENTION

The present invention is directed to a nonwoven wipe having a reversiblecolor-changing sanitizer indicator for multiple uses and recharges. Thenonwoven wipe can be used to wipe down tables and countertops, forexample, until the concentration of sanitizer in the wipe falls below athreshold concentration. At that point, the color of the nonwoven wipechanges from a first color to a second color. The nonwoven wipe can thenbe recharged, for example by immersing it in a bucket of sanitizersolution. The recharged nonwoven wipe then changes back to the firstcolor, and can be used until the concentration of sanitizer falls to thethreshold concentration and the color again changes to the second color.The nonwoven wipe is recharged again, and the cycle is repeated untilthe nonwoven wipe becomes exhausted due to soiling or damage, or thecleaning task is completed.

The nonwoven wipe includes a cloth-like nonwoven fabric formed, at leastin part, of absorbent nonwoven fibers formed from cellulose or anothersuitable material. The absorbent fibers can be formed to rayon. Thenonwoven fibers can be used alone or in combination with reinforcingnonwoven fibers, which need not be absorbent. The structural fibers canbe formed of polyester or another suitable material.

The cloth-like nonwoven fabric is coated with a reversiblecolor-changing ink formulation that durably binds itself to the nonwovenfabric, and remains bound during repeated use cycles. The reversiblecolor-changing ink formulation includes about 10-50% by weight of apolymer binder, about 10-50% by weight of a plasticizer, about 10-50% byweight of a wetting agent, about 0-10% by weight of an ionic stabilizer,and about 1-10% by weight of an anionic indicator compound, based on dryweight of the ink formulation. The ingredients of the ink are dissolvedin a volatile organic solvent for application to the cloth-like nonwovenfabric. When fully dried, the ink does not leach or otherwise escapefrom the nonwoven wipe, and can reversibly change color to indicate therelative concentration of sanitizer in the nonwoven wipe.

The nonwoven wipe is impregnated with a sanitizer, suitably one that isbased on a quaternary ammonium compound. The nonwoven wipe may beprovided with the sanitizer already impregnated. Alternatively, thenonwoven wipe may be provided without sanitizer, and may be impregnatedwith sanitizer by the user. In a preferred embodiment, the desiredminimum concentration of quaternary ammonium compound in the nonwovenwipe (which causes color change) may range from about 180 ppm to about250 ppm, based on the dry weight of the nonwoven wipe. The nonwoven wipeis impregnated with a higher amount of quaternary ammonium compound, asexplained below. When the concentration of quaternary ammonium compoundfalls to the threshold level during use, the resulting color changeindicates the need to recharge. The quaternary ammonium compound isoften provided in an aqueous solution, and can be applied by dipping thenonwoven wipe in a bucket containing the sanitizer solution.

By reversibly changing color during use, the nonwoven wipe provides areliable indication of when it needs to be recharged during use, due todepletion of the sanitizer. By maintaining proper sanitizerconcentration, the nonwoven wipe can be used for as long as it is neededto complete the task at hand, or until the wipe becomes damaged orheavily soiled.

With the foregoing in mind, it is a feature and advantage of theinvention to provide a nonwoven wipe having a reversible color-changingsanitizer indicator, which nonwoven wipe can be recharged and usedseveral times while providing a reliable indication of sanitizerconcentration.

It is also a feature and advantage of the invention to provide anonwoven wipe having extended use life due to the presence of a durableindicator which repeatedly and reversibly indicates changes in sanitizerconcentration in the nonwoven wipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a nonwoven wipe according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a reversible color-changing sanitizer indicatingnonwoven wipe 8 of the invention includes a cloth-like nonwoven fabric10 including a plurality of nonwoven fibers 12. The nonwoven fibers 12include absorbent nonwoven fibers 14 and may optionally includereinforcing nonwoven fibers 16, which may be absorbent or nonabsorbent.The absorbent nonwoven fibers 14 may be formed from cellulose or anothersuitable absorbent material. Suitable cellulose fibers include withoutlimitation fibers formed from wood, cotton, silk, straw, hay, and otherplants. Rayon fibers are particularly suitable for the absorbentnonwoven fibers 14. Rayon fibers are textile filaments made from cottonlinters, wood chips or other cellulose by treating them with causticsoda and carbon disulfide, and passing the resulting viscose solutionthrough spinnerets.

When used, the reinforcing nonwoven fibers 16 may be formed from strong,flexible polymeric material. Suitable polymeric materials includewithout limitation polyester, polypropylene, high density polyethylene,linear low density polyethylene, polyamides, polytetrafluoroethylene,and combinations thereof. The cloth-like nonwoven fabric 10,specifically the nonwoven fibers 12, may include 50-100% by weight ofthe absorbent nonwoven fibers 14 and about 0-50% by weight of thereinforcing nonwoven fibers 16, suitably about 55-90% by weight of theabsorbent nonwoven fibers 14 and about 10-45% by weight of thereinforcing nonwoven fibers 16, or about 60-80% by weight of theabsorbent nonwoven fibers 14 and about 20-40% by weight of thereinforcing nonwoven fibers 16.

In accordance with the invention, the cloth-like nonwoven fabric 10 iscoated with a reversible color-changing ink formation that is sensitiveto the concentration of quaternary ammonium compound in the nonwovenwipe 8. On a dry weight basis, the color-changing ink formulationincludes about 10-50% by weight of a polymer binder, suitably about20-45% by weight, or about 30-40% by weight. The polymer binder helpsbond the nonwoven fibers 12 of the fabric 10 together, and also forms adurable bond between the nonwoven fabric 10 and the remainingingredients of the color changing ink formulation. The relatively highamount and bond strength of the binder polymer help ensure that thereversible color-changing ingredients of the ink formulation will remainintact and functional for the useful life of the nonwoven wipe 8.

Suitable polymeric binder compounds include without limitation celluloseacetate and cellulose acetate derivatives. One suitable polymeric binderis cellulose acetate having a number average molecular weight of about30,000, sold by Aldrich Chemical Co. Other suitable polymeric bindersare cellulose acetate butyrates having number average molecular weightsof about 16,000, 20,000 and 30,000 sold by Eastman Chemical Co. underthe trade names CAB 551-0.01, CAB 553-0.4 and CAB 551-0.2, respectively.Other suitable polymeric binders include without limitation celluloseacetate propionate, polymers of carboxymethyl cellulose, polymers ofethyl cellulose, polymers of nitrocellulose, and combinations thereof.

The reversible color-changing ink formulation also includes about1.0-50% by weight plasticizer on a dry weight basis, suitably about15-40% by weight, or about 20-30% by weight. The plasticizer helpsmaintain the flexibility of the nonwoven wipe 8 with the color changingink formulation applied, i.e., by softening the color-changing inkformulation so that it does not stiffen the nonwoven wipe 8. Suitableplasticizers include without limitation dibutyl phthalate and triethylcitrate sold by Aldrich Chemical Co. Other suitable plasticizers includewithout limitation bis-(2-butoxylethyl) adipate, bis-(2ethylhexyl)sebacate, diethyl phthalate, and combinations thereof.

The reversible color-changing ink formulation also includes about 10-50%by weight of a wetting agent on a dry weight basis, suitably about15-40% by weight, or about 20-35% by weight. The wetting agent causesthe color-changing ink formulation to spread, cover and (to an extent)envelop the nonwoven fibers 12 of the fabric 10, resulting in moredurable bonding between the color-changing ink formulation and thenonwoven fabric 10. Suitable wetting agents include without limitationethylene glycol and 2-ethoxy ethanol sold by Aldrich Chemical Co. Othersuitable wetting agents include without limitation triethylene glycol,sorbitol, and combinations thereof.

The reversible color-changing ink formulation may include about 0-5% byweight, suitably about 0-3% by weight of an ionic stabilizer, based onthe dry weight of the ink formulation. When used, the ionic stabilizermay be a quaternary ammonium compound, and may be chemically similar oridentical to the quaternary ammonium compound used in the sanitizersolution that is later impregnated into the nonwoven wipe 8. When used,the concentration of ionic stabilizer should not be so great as toprevent the color-changing ink from responding to the concentration ofquaternary ammonium compound resulting from the sanitizer solution inthe nonwoven wipe. Suitable ionic stabilizers include without limitationdi (long chain alkyl) dimethyl ammonium chlorides; N-methyl-N, N-bis(long chain alkanoyl oxyethyl)-N-(2-hydroxymethyl) ammoniummethylsulfates; vinylbenzyl dimethylcocoammonium chlorides; and methyltrioctyl ammonium chlorides. One suitable anionic stabilizer isSTEPANQUAT® 2125M-P40, available from Stepan Company. This product is amixture of about 50% by weight N-alkyl (60% C14, 30% C16, 5% C12 and 5%C18) dimethyl benzyl ammonium chlorides and about 50% by weight N-alkyl(68% C12 and 32% C14) dimethyl ethyl benzyl ammonium chlorides.

The reversible color-changing ink formulation includes about 1-10% byweight of an anionic indicator compound on a dry weight basis, suitablyabout 1.5-7% by weight, or about 2-4% by weight. The amount of anionicindicator is small relative to the amount of binder polymer, thusensuring a durable, permanent bond to the nonwoven fabric 10. Theanionic indicator reversibly changes color when the amount of quaternaryammonium compound in the sanitizing solution surpasses a predeterminedlevel in either direction. The anionic indicator causes the ink tochange from a first color to a second color during use of the nonwovenwipe, when the concentration of quaternary ammonium compound in thenonwoven wipe falls below a selected level. Then, when the nonwoven wipeis recharged with the quaternary ammonium compound based sanitizer, theanionic indicator causes the ink to change from the second color back tothe first color.

The specific type of anionic indicator used may depend on the desiredthreshold concentration of anionic indicator that triggers the colorchange. Different anionic indicators trigger color changes at differentconcentrations of quaternary ammonium compounds. More than one anionicindicator may also be used, if it is desired to indicate two or morecolor changes at two or more different concentrations of quaternaryammonium compounds. The anionic indicator(s) may include withoutlimitation one or a plurality of compounds selected from bromothymolblue, thymol blue, m-cresol purple, xylenol blue, xylenol orange, phenolred, and combinations thereof.

The reversible color-changing ink formulation may also include about1-25% by weight, suitably about 10-20% by weight of a particulateinorganic filler. It has been found that inclusion of a filler helpsimprove the intensity of the color change, so that the color changebecomes more apparent and visible. Suitable particulate fillers includewithout limitation silicon dioxide, titanium dioxide, calcium carbonate,and combinations thereof. One particularly suitable filler is amorphoussilica (amorphous silicon dioxide) available from W.R. Grace & Co. underthe trade name SYLOID® C 803.

The ink ingredients can be mixed together in a volatile organic solventin an amount of about 15-50% by weight total ink ingredients based onthe combined weight of the ink ingredients and solvent. Suitablevolatile organic solvents which also dissolve the ink ingredientsinclude without limitation n-propyl acetate and volatile ketones, forexample acetone, methylethyl ketone, toluene, tetrahydrofuran, ethylacetate, and combinations thereof. The color-changing ink solution canbe applied to the nonwoven fabric 10 by dipping, dripping, immersion,spray coating, brush coating, roll coating, printing, or any suitabletechnique. The coated nonwoven fabric 10 can then be dried in thepresence of heat and/or vacuum to remove the volatile organic solvent,leaving the color-changing ink composition firmly bonded to the nonwovenfabric 10. Drying temperatures of about 40° C. to about 60° C. aregenerally sufficient. The drying times may range from several minutes toseveral hours depending on the particular composition, structure andbasis weight of the nonwoven fabric 10, and on the specific compositionof the color-changing ink composition.

After drying, the reversible color-changing ink composition shouldconstitute about 1.0-10% by weight, suitably about 3-5% by weight of thenonwoven wipe 8. These amounts are based on the weight of the drynonwoven wipe 8, before it is charged with a quaternary ammoniumcompound-based sanitizer solution.

During use, the nonwoven wipe 8 is typically charged with quaternaryammonium compound-based sanitizer solution by dipping or immersing thenonwoven wipe 8 in a cleaning bucket that contains the sanitizersolution, typically diluted with water. The nonwoven wipe 8 may also beprovided as a precharged wipe which is already impregnated withquaternary ammonium compound-based sanitizer solution. One suitablequaternary ammonium compound-based sanitizer is the above-describedSTEPANQUAT® 2125M-P40, available from Stepan Company. Again, thisproduct is a mixture of about 50% by weight N-alkyl (60% C14, 30% C16,5% C12 and 5% C18) dimethyl benzyl ammonium chlorides and about 50% byweight N-alkyl (68% C12 and 32% C14) dimethyl ethyl benzyl ammoniumchlorides. The product is available as a powder. For use as a sanitizingsolution, the powder can be added to water in an amount which results inan aqueous solution having a quaternary ammonium compound concentrationof about 0.195-0.225% by weight.

The aqueous sanitizer solution is applied to the nonwoven wipe 8, asnoted above, by dipping or immersing the nonwoven wipe 8 in thesanitizer solution. The amount of sanitizer solution absorbed by thenonwoven wipe 8 depends on the structural characteristics, basis weightand absorbent characteristics of the nonwoven wipe 8. As explainedabove, the sanitizer solution may contain about 180 to about ppm,suitably about 180 to about 250 ppm of the quarternary ammoniumcompound. When fully charged, the nonwoven wipe 8 will typically containabout 150-350% by weight, suitably about 250-300% by weight of theaqueous sanitizer solution based on the dry weight of the nonwoven wipe8. As explained above, the sanitizer solution may contain about 180 toabout 400 ppm, suitably about 180 to about 250 ppm of the quaternaryammonium compound. The free quaternary ammonium compound content of thenonwoven wipe 8, based on the dry weight of the nonwoven wipe 8, issuitably about 300 to about 1200 ppm, or about 500 ppm to about 1000ppm. The term “free quaternary ammonium component content” refers to theamount of quaternary ammonium compound contributed by the sanitizersolution, and does not include any quaternary ammonium compoundcontained in the color-changing ink composition as an ionic stabilizer.

To determine a threshold concentration of free quaternary ammoniumcompound in the nonwoven wipe that causes a particular applied inkcomposition to change from a first color to a second color during use,the following procedure can be followed. First, the weight “D” of thedry nonwoven wipe 8 with applied ink composition is measured. Then, thenonwoven wipe 8 is impregnated with aqueous sanitizer solution andweighed, to determine the fully charged weight “C”. The amount “Q” ofquaternary ammonium compound in the fully charged nonwoven wipe 8 isdetermined by multiplying the weight ratio “R” of quaternary ammoniumcompound in the aqueous cleaning solution by the difference between Cand D, according to the following equation:

Q=R(C−D)

The fully charged concentration “P” (in parts per million) of quaternaryammonium compound in the nonwoven wipe 8, based on the dry weight of thenonwoven wipe 8, is therefore (Q/D)×10⁶.

To determine the threshold concentration of quaternary compound thattriggers a color change during use, simply wipe the nonwoven wipe 8across a table or countertop until the color begins to change from thefirst color to the second color, weigh the nonwoven wipe 8 again todetermine the depleted weight “L.” The threshold concentration T (inparts per million) can be determined from the following equation:

$T = {P\frac{\left( {L - D} \right)}{\left( {C - D} \right)}}$

By following the foregoing procedure, different ink compositions can betested for a particular nonwoven wipe 8 to develop an ink compositionwhich changes color at a desired threshold concentration T. In mostinstances, the desired threshold concentration T for a nonwoven wipe 8is about 180-250 ppm, suitably about 190-220 ppm. When the concentrationof quaternary ammonium compound in the nonwoven wipe 8 falls below thethreshold level, the nonwoven wipe 8 becomes less effective forsanitizing applications, and it becomes important to recharge thenonwoven wipe 8 with sanitizer solution.

Once the threshold concentration T has been determined for a particularink composition, a much simpler procedure can be used to determine therelative sensitivity of different ink compositions, i.e. whetherdifferent ink compositions will change color at higher or lower levelsof quaternary ammonium compound. To determine the relative sensitivityof different ink compositions, sanitizer solutions containing severaldifferent concentrations of quaternary ammonium compound can be preparedin separate buckets or containers. For example, solutions containingquaternary ammonium compounds at 0 ppm, 50 ppm, 125 ppm, 250 ppm, 500ppm and 1000 ppm can be prepared. Then, nonwoven wipes coated withdifferent color-changing ink compositions can each be dippedsequentially into the sanitizer solutions, beginning with the lowestconcentrations, to determine the concentration of quaternary ammoniumcompound that triggers a color change. While this simpler procedure canbe used to determine if one ink changes color at a higher or lowerquaternary ammonium content relative to another ink, it will notdetermine the threshold concentration T of quaternary ammonium compoundin a nonwoven wipe 8. It is also within the scope of the invention toprovide a method of cleaning a surface. The method includes the steps ofproviding a nonwoven wipe including a nonwoven fabric and a reversiblecolor-changing ink formulation bound to the nonwoven fabric. A sanitizersolution is provided, and the nonwoven wipe is impregnated with thesanitizer solution. The surface is wiped with the nonwoven until thecolor-changing ink formulation changes from a first color indicatingsufficient sanitizer solution to a second color indicating insufficientsanitizer solution. The nonwoven wipe is then impregnated withadditional sanitizer solution at least until the color-changing inkformulation changes back to the first color.

EXAMPLES

The following reversible color-changing ink compositions were prepared.

Ingredient Example 1 Ink Example 2 Ink Bromothymol Blue 0.3 g XylenolBlue 0.3 g Cellulose Acetate 3.7 g 3.7 g Dibutyl Phthalate 2.8 g 2.8 gStepan 2125M 0.4 g 0.4 g Ethylene Glycol 2.8 g 2.8 g Acetone 30 mlMethyl Ethyl Ketone 30 ml

The ingredients of each ink composition were mixed until the celluloseacetate fully dissolved and all ingredients were incorporated. Ifnecessary, more solvent may be added to achieve desired viscosity. Eachink composition was printed in a pattern on a 24 in×24 in (61 cm×61 cm)nonwoven wipe composed of 80% by weight rayon and 20% by weightpolyester fibers. The coated wipe was dried in an oven at 50° C. for 12hours. The wipe was then rinsed in deionized water to remove any excessink composition. Each coated wipe was then placed in the followingsolutions and the following colors were observed.

Solution Example 1 Wipe Example 2 Wipe Water Yellow Orange-Brown AqueousQAC Green-Blue Dark Green Sanitizer (220 ppm)

The colors reversed when the wipes initially placed in the aqueous QACsanitizer were then placed in water, and vice versa. Only slight fadingof colors was observed after four cycles, due to some leaching of theink from the wipes. Most of the ink remained durably bound, as evidencedby the continued reversible color change.

While the embodiments of the invention described herein are exemplary,various modifications and improvements can be made without departingfrom the spirit and scope of the invention. The scope of the inventionis indicated by the appended claims, and all changes that fall withinthe meaning and range of equivalents are intended to be embracedtherein.

We claim:
 1. A method of making an article having reversiblecolor-changing properties, comprising the steps of: providing a fabricformed of flexible polymeric material; applying a solution including areversible color-changing ink formulation and a solvent to the fabric;drying the solution on the fabric to remove the solvent; and durablybinding the reversible color-changing ink formulation to the fabric;wherein the reversible color-changing ink formulation comprises apolymer binder, a plasticizer, a wetting agent and an anionic indicatorcompound, and the drying causes the reversible color-changing inkformulation to durably bind to the fabric.
 2. The method of claim 1,further comprising the step of heating the fabric to perform the drying.3. The method of claim 2, wherein the fabric is heated to a temperatureof about 40° C. to about 60° C.
 4. The method of claim 1, furthercomprising the step of applying a vacuum to the fabric.
 5. The method ofclaim 1, wherein the reversible color-changing ink formulation comprisesabout 10-50% by weight of the polymer binder, about 10-50% by weight ofthe plasticizer, about 10-50% by weight of the wetting agent, and about1-10% by weight of the anionic indicator compound, based on a dry weightof the reversible color-changing ink formulation.
 6. The method of claim1, wherein the solution comprises about 15-50% by weight of thereversible color-changing ink formulation.
 7. The method of claim 1,wherein the solvent is selected from the group consisting of n-propylacetate, acetone, methylethyl ketone, toluene, tetrahydrofuran, ethylacetate, and combinations thereof.
 8. The method of claim 1, wherein thepolymer binder comprises a polymer selected from the group consisting ofcellulose acetate, cellulose acetate derivatives, carboxymethylcellulose, ethyl cellulose, nitrocellulose, and combinations thereof. 9.The method of claim 1, wherein the plasticizer comprises a compoundselected from the group consisting of dibutyl phthalate, triethylcitrate, bis-(2-butoxylethyl) adipate, bis-(2-ethylhexyl) sebacate,diethyl phthalate, and combinations thereof.
 10. The method of claim 1,wherein the wetting agent comprises a compound selected from the groupconsisting of ethylene glycol, 2-ethoxy ethanol, triethylene glycol,sorbitol, and combinations thereof.
 11. The method of claim 1, whereinthe anionic indicator comprises a compound selected from the groupconsisting of bromothymol blue, thymol blue, m-cresol purple, xylenolblue, xylenol orange, phenol red, and combinations thereof.
 12. Themethod of claim 1, wherein the flexible polymeric material is selectedfrom the group consisting of polyester, polypropylene, high densitypolyethylene, linear low density polyethylene, polyamides,polytetrafluoroethylene, and combinations thereof.
 13. A method ofimparting reversible color-changing properties to a polymeric article,comprising the steps of: providing a polymeric article; applying asolution including a reversible color-changing ink formulation to thepolymeric article; drying the solution on the polymeric article; anddurably binding the reversible color-changing ink formulation to thepolymeric article; wherein the reversible color-changing ink formulationcomprises a polymer binder, a plasticizer, a wetting agent and ananionic indicator compound, and the drying causes the reversiblecolor-changing ink formulation to durably bind to the polymeric article.14. The method of claim 13, further comprising the step of contactingthe polymeric article with a free quaternary ammonium compound solution,wherein the anionic indicator compound causes the reversiblecolor-changing ink formulation to change back and forth between a firstcolor when the free quaternary ammonium compound exceeds a thresholdconcentration and a second color when the free quaternary ammoniumcompound falls below the threshold concentration.
 15. The method ofclaim 14, wherein the threshold concentration is about 190-220 ppm. 16.The method of claim 13, wherein the polymer binder comprises a polymerselected from the group consisting of cellulose acetate, celluloseacetate derivatives, carboxymethyl cellulose, ethyl cellulose,nitrocellulose, and combinations thereof.
 17. The method of claim 13,wherein the plasticizer comprises a compound selected from the groupconsisting of dibutyl phthalate, triethyl citrate, bis-(2-butoxylethyl)adipate, bis-(2-ethylhexyl) sebacate, diethyl phthalate, andcombinations thereof.
 18. The method of claim 13, wherein the wettingagent comprises a compound selected from the group consisting ofethylene glycol, 2-ethoxy ethanol, triethylene glycol, sorbitol, andcombinations thereof.
 19. The method of claim 13, wherein the anionicindicator comprises a compound selected from the group consisting ofbromothymol blue, thymol blue, m-cresol purple, xylenol blue, xylenolorange, phenol red, and combinations thereof.
 20. A method of monitoringa concentration of quaternary ammonium-containing compound using apolymeric article, comprising the steps of: contacting a quaternaryammonium compound-containing solution to the polymeric article; usingthe polymeric article, causing a reduction in the quaternary ammoniumcompound below a threshold concentration wherein the polymeric articlechanges from a first color to a second color; and adding more of thequaternary ammonium compound-containing solution to the polymericarticle until the quaternary ammonium compound exceeds the thresholdconcentration wherein the polymeric article changes from the secondcolor back to the first color; wherein the polymeric article comprises areversible color-changing ink formulation durably bound thereto.